Differential Expression of RNA and Protein of the Three Pore-forming Subunits of the Amiloride-sensitive Epithelial Sodium Channel in Taste Buds of the Rat

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Abstract
Salt taste signals from the rat anterior tongue are probably transduced via epithelial sodium channels (ENaCs) residing in the apical cellular pole of taste cells. The signals are blocked by mucosal amiloride in low μM concentrations. In contrast, the rat vallate papilla does not contribute to amiloride-blockable salt taste. Two approaches were used to probe for the three subunits of ENaC in the anterior and posterior tongue of the rats in sodium balance. (a) Immunohistochemistry with antibodies against ENaC subunits and against amiloride binding sites. In the anterior tongue, reactivity for α-, β-, and γ-subunits was present in taste buds and lingual epithelium. In the posterior tongue vallate papilla, reactivity for α-subunit and for amiloride binding sites was easily demonstrable, whereas that for β-subunit and especially for γ-subunit was weaker than in the anterior tongue. (b) RT-PCR techniques were used to probe for the presence of ENaC subunit mRNA. In isolated taste buds of the anterior tongue, mRNA of all three subunits was found, whereas in isolated taste buds of the vallate papilla only mRNA of the α-subunit was easily detectable. That of β- and γ-subunits was much less abundant. RNA of all three subunits was abundant only in taste buds of the anterior tongue. Therefore, subsets of elongated taste cells do express ENaC, but regional differences exist in the transcription and expression of subunits. The regional differences suggest that amiloride-sensitive salt taste, which requires all three subunits, is present in the anterior but not the posterior tongue of rats, as functional studies indicate.